Medicament delivery devices for delivering medicaments to a patient generally comprise a reservoir for the medicament and driving means for delivering the medicament to the patient. The reservoir can be pre-filled with a medicament, or the device can be provided with means for filling the reservoir. The reservoir may be configured in many different ways; however, general types of reservoirs can be identified.
The best known and mostly used type of injection device for the treatment of different medical conditions, such as insulin treatment of type 1 or 2 diabetes, is the “pen”-formed device where the pen can be considered a manually actuated pump serving as the delivery means for a drug contained in a cartridge, generally in the form of a non-deformable cylindrical or columnar syringe comprising a displaceable piston. Although originally designed for the pen-type of devices, this type of reservoir has also been used in delivery pump devices comprising driving means allowing the drug to be expelled from the reservoir in a controlled manner. Although conventional drug cartridges are relatively inexpensive, their use in drug delivery devices has hitherto been associated with a number of disadvantages such as difficulties in modifying the general cylindrical form or the problems associated with the mechanical plunger means for driving the piston, such plunger driving means being both expensive and bulky adding to the cost and size of the delivery device. Other means than driving the piston by a mechanically advanced plunger have been suggested and will be discussed below.
Another type of reservoir is in the form of an expansible-contractible chamber arranged within a housing member, the interior of the housing including a flexible liquid-impermeable membrane defining a first expansible-contractible chamber between it and a first non-deformable section of the housing, and a second expansible-contractible chamber defined between it and a second non-deformable section of the housing. The first chamber serves as a reservoir for receiving the drug to be delivered, whereas the second chamber typically serves as a gas-pumping chamber for controlling the delivery of the drug from the reservoir. An example of such a reservoir is disclosed in U.S. Pat. No. 5,527,288.
A further type of reservoir is in the form of a flexible bag, however, although many i.v. infusion drugs are supplied in such containers, they have hitherto not been used extensively as reservoirs in portable delivery pump devices.
With respect to the driving means for moving a drug out of a container, in principle two different driving approaches can be used, i.e. either “pushing” or downstream “sucking”.
“Pushing” in this respect covers any action which by reducing the internal volume of a reservoir drives out the therein contained drug. The pushing means may be in the form of mechanical means, for example a motor driven plunger rod acting on a piston in a cylinder reservoir as described above, or it may be in the form of gas generating means, in which case the gas may act on an expansible-contractible chamber as described above with respect to U.S. Pat. No. 5,527,288, or the gas may act directly on a piston in a cylinder reservoir as disclosed in WO 98/57683.
A further dispensing device based on gas generating means is known from U.S. Pat. No. 5,938,640 disclosing a dispenser comprising a variable-volume drug reservoir and a small water reservoir, the water being conducted to a gas-generating pump where it is used for producing a metered amount of a gas which subsequently is used to expel drug from the drug reservoir. The drug and water reservoirs are provided in a reservoir module and the gas-generating pump is provided in a pump module.
As appears, the gas generating means and the associated connecting means for allowing the gas to act on the reservoir provides for a relatively flexible design in which the actual form and configuration of the different components may be adapted specifically to fit the actual specification for a given delivery device. However, a major disadvantage associated with gas-based driving means is the susceptibility to pressure changes in the surrounding environment of use. More specifically, a pressure drop outside the gas-pumping chamber will result in expansion of the therein contained gas which inevitably will result in uncontrolled expelling of drug from the reservoir. Evidently, such a situation is not merely hypothetical but will take place during, for example, a flight in an aeroplane without pressure cabin or during mountain walking or climbing. Also normal atmospheric depressions may of an order which will influence the function of the device. Contrary, a pressure rise will result in a corresponding compression of the gas in the gas-driving chamber and consequently result in a diminished amount of drug being supplied to the patient. Evidently, it would be possible to prevent such undesired consequences of external pressure variations, for example by stopping gas generation and sealing off the gas pumping chamber, however, to provide the necessary valve means, pressure sensor means and control means would considerably add to the complexity and cost of the delivery device, just as a closed-down system would be non-functional until “normal” pressure conditions are re-established. Indeed, it would be possible to operate such a system also under varying external pressure condition, however, this would necessitate controlling the actual output flow, this further adding to the complexity.
A different principle is known from DE-A1-37 39 657 disclosing a bedside infusion set-up. In order to avoid the need for a traditional pump a syringe plunger rod is hydraulically driven. More specifically, a flexible bag containing a drive liquid is suspended over the syringe and fed by gravitational force to a chamber moving the plunger, this providing a simple pump means.
“Sucking” in this respect covers any action by which a drug is drawn from a reservoir by applying a negative pressure (relative to the pressure in the reservoir) to an outlet opening of the reservoir. A traditional type of pump used in the context of administering a drug or fluid to a patient is the peristaltic pump acting on a flexible tube portion, this arrangement preventing the pump means (except for the tube) to come into contact with the drug. FR-A-2 753 103 discloses a medical pump device incorporating such a peristaltic pump.
Another type of pump used in this context is the conventional valve pump comprising a displacing structure (e.g. a piston or a pump membrane) cooperating with inlet and outlet valves. Such a pump may be formed with separate actuation means driving the valves and the displacing structure formed integrally with a disposable reservoir and its associated tubing, or it may be in the form of a micro pump in direct contact with the drug. The latter type of pump would mainly be relevant as a disposable unit as the need for cleaning a pump is not considered desirable
Depending on the type of suction pump used, a number of disadvantages are associated therewith. Depending on the type of reservoir used, it may be necessary to apply very high (relative) negative pressures, for example when drawing a drug from a conventional syringe-piston cartridge. In fact, many such standard cartridges have a frictional resistance between the (rubber) piston and the (glass) cylinder wall which could not be overcome even by an absolute vacuum provided by the pump. Pumps relying on a disposable portion in contact with the drug and a durable pump drive means are typically bulky as well as expensive, whereas an integrated disposable micro pump would add to the cost of the disposable cartridge as such.
A further problem when using a suction pump is the risk for damaging a pressure sensitive drug as it is sucked through the pump, which especially is a problem when using micro pumps in which the drug is forced through narrow passageways. Another problem is the risk of contaminating the drug with substances from structures with which the drug comes into contact, e.g. the displacing structure and the valves. The other way round, the drug may also be harmful to these structures.
Having regard to the above discussion of known devices and systems, there exists a need for a new and improved concept for a delivery device and system which provide a high degree of safety, ease of use and compactness as well as a high degree of flexibility in respect of using different types of reservoirs without having to substantially redesign the delivery device and its different components. The device should be safe and reliable in use under most external pressure conditions, it should be gentle to the drugs to be infused as well as easy to use, compact in size and inexpensive to manufacture. Further, the general concept should allow the manufacturer to provide a high degree of flexibility in a cost effective and efficient manner.
Correspondingly, it is an object of the present invention to provide a pump which overcomes one or more of the identified deficiencies and provides a solution to one or more of the identified needs.